Reusable zone

ABSTRACT

Implementations of the disclosed technology may respond to a discovery request according to the origination of the discovery request. In these implementations, a discovery request for a connection to a device assigned to a reusable zone may be obtained. If the discovery request does not originate from a local switch group, the discovery response may indicate that there is no device at the connection.

BACKGROUND

Zoning may be used in some networks to control access between networkdevices. For example, a SAS (Serial Attached Small Computer SystemInterface (SCSI)) domain may include initiators, such as host busadaptors (HBAs) or controllers; targets, such as storage devices; andswitches, such as expanders, connecting the initiators and devices.Zoning may be used to control which targets different initiators areable to access. In some protocols, access between zones may becontrolled by a zoning policy. For example, in one implementation,devices in Zone A may be given access to devices in Zones A and B, butdevices in Zone C may be only able to access devices in Zone C.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain examples are described in the following detailed description andin reference to the drawings, in which:

FIG. 1 illustrates an example network fabric implementation utilizingzone reuse;

FIG. 2A illustrates an example method of providing a discovery responsefor a device assigned to a reusable zone;

FIG. 2B illustrates an example method of providing a discovery responsefor a device assigned to a non-reusable zone;

FIG. 3 illustrates an example switch including a controller to generatea discovery response to a discovery request for a device assigned to areusable zone; and

FIG. 4 illustrates an example zone manager including a non-transitorycomputer readable medium storing instructions for partitioning a networkinto switch groups, reusable zones, and non-reusable zones.

DETAILED DESCRIPTION OF SPECIFIC EXAMPLES

Some zoning-enabled networking protocols may allow only a limited numberof zones. For example, SAS version 2 (SAS-2) uses a one byte field tolabel zones and reserves the first 8 zones, which limits the number ofcustomizable zones to 248. As the number of devices in a networkincreases, a network administrator may exhaust the number of availablezones, preventing the network administrator from implementing otherwisedesirable zoning schemes.

Some aspects of the disclosed technology may allow zone reuse in anetwork. For example, FIG. 1 illustrates an example network fabric 100implementation utilizing zone reuse. The fabric 100 includes a pluralityof devices 108, . . . , 115 interconnected by switches 103, . . . , 107.For example, in a SAS fabric 100, the devices 108, . . . , 115 mayinclude target devices and initiator devices, and the switches 103, . .. , 107 may include expanders. As another example, in an Fibre Channel(FC) or FC over Ethernet (FCoE), the switches 103, . . . , 107 may benetwork switches.

The fabric 100 may be divided into switch groups 101, 102. For example,switches S1 103, S2 104, S3 105 may be assigned to a first switch group101, and switches S4 106, S5 107 may be assigned to a second switchgroup 102. Additionally, available zone labels may be divided into anon-reusable zone group and a reusable zone group. In the illustratedexample, zones {8, . . . , 255} are available, zones {8, . . . , 150}are assigned to the reusable zone group and zones {151, . . . , 255} areassigned to the non-reusable zone group. In some implementations, zoneidentification numbers in the reusable zone group may be reused in eachswitch group 101, 102. Accordingly, in these implementations, each zonenumber in the reusable zone group is local to the switch groups 101,102. Different switch groups 101, 102 may reuse the zone numbers in thereusable zone group for different zones. In contrast, in someimplementations, zone identification numbers in the non-reusable areused globally across the entire fabric 100. In these implementations,only a single zone in the fabric 100 may have a zone number in thenon-reusable zone group.

In some implementations, the switches 103, . . . , 107 may implementaccess control rules where: (1) a device in a reusable zone can accessother devices in its local switch group if zone permissions otherwiseallow, but cannot access devices outside its local switch group; and (2)a device in a non-reusable zone can access other devices in its localswitch group and devices in non-reusable zones in other switch groups ifthe zone permissions otherwise allow, but cannot access devices inreusable zones outside its local switch group.

As an example, a zone manager 116 provide zone permissions 117 to theswitches 103, . . . , 107—for example, in the form of permissiontables—permitting devices in zones 8 and 151 to communicate with eachother, and permitting devices in zones 8 and 9 to communicate with eachother. In this example, device D7 114 is permitted to access device D5112, because device D5 112 is in its local switch group 102.Additionally, device D7 114 is allowed to access device D4 111 becausedevice D4 111 is assigned to the non-reusable zone 151. However, deviceD7 114 is not allowed to access devices D1 108 and D3 110 because theyare assigned to reusable zone 8 and outside device D4's 111 local switchgroup 102. Further, device D5 112 is permitted to communicate withdevices D6 113 and D8 115, because they are assigned to reusable zonesand are all in the same switch group 102. However, devices D1 108 and D3110 are not permitted to communicate with devices D6 113 and D8 115because they are in different switch groups 101, 102. Accordingly, inthis example, devices D1 108 and D3 110 are in a different zone thandevice D5 112, even though all three devices 108, 110, 112 have the samezone identification number. Accordingly, the zone identification number{8} has been reused in different switch groups 101, 102 of the fabric100. In contrast, devices D2 109, D4 111, and D7 114 are in the samezone. Accordingly, the zone identification number {151} is non-reusablein the fabric 100.

In some implementations, zoning may be implemented during the discoveryprocess to implement the access control rules. For example, device D1108 may be connected to a transceiver n of the switch S2 104. During adiscovery process, device D4 111 may send a discovery request to switchS2 to discover whether there is a device connected to transceiver n.Switch S2 104 may prevent access to device D1 by responding that thereis no device connected to transceiver n.

In some implementations, the zone manager 116 may manage the assignmentof switches 101, . . . , 107 into switch groups 118. For example, thezone manager 116 may obtain the switch group assignment 118 and assigneach switch 103, . . . , 107 to its assigned switch group by providing aswitch group identification to each switch 103, . . . , 107.Additionally, the zone manager 116 may manage the assignment 119 ofavailable zones into reusable zone groups and non-reusable zone groups.For example, the zone manager 116 may transmit a list of the reusablezones and a list of the non-reusable zones to the each switch 103, . . ., 107.

In some implementations, the zone manager 116 may provide an input for auser to provide the switch group assignment 118 and zone groupassignment 119. In other implementations, the zone manager 116 mayobtain an accessibility assignment for the devices 108, . . . , 115 andmay generate the switch group assignment 118 and zone group assignment119 from the accessibility assignment. For example, a user may providethe accessibility assignment as an allocation of the devices 108, . . ., 115 into groups that are permitted to communicate. The zone manager116 may then inspect the topology of the fabric 100 and attempt togenerate a switch group assignment 118 and zone group assignment 119that fulfills the accessibility assignment.

In some implementations, the switch groups 101, 102 are continuous. In acontinuous switch group, a communication between two devices connectedto the switch group does not need to be routed through a switch outsidethe switch group. In other implementations, the switch groups 101, 102may be discontinuous.

FIG. 2A illustrates an example method of providing a discovery responsefor a device assigned to a reusable zone. For example, a switch in anetwork fabric may perform the illustrated method when receivingdiscovery requests from devices in the network. For example, a switch103, . . . , 107 in a fabric 100, such as a SAS expander, as describedwith respect to FIG. 1 may perform the illustrated method.

Block 201 of the example method includes obtaining a discovery requestfor a connection to a device assigned to a reusable zone. For example, aswitch performing the illustrated method may have a plurality ofconnections to connect to other devices or switches. For example, in aSAS fabric, an expander may perform block 201 by receiving a SerialManagement Protocol (SMP) DISCOVER request for a physical or logicaltransceiver (PHY) connected to a device assigned to a reusable zone. Asanother example, a switch may perform block 201 by receiving a discoveryrequest for a port connected to a device assigned to a reusable zone.

Block 202 of the example method includes determining if the discoveryrequest originates in a local switch group. For example, in a SASfabric, an expander may determine if the discovery request wastransmitted by an initiator device connected to another expander in thelocal expander group.

In some implementations, a switch may use a switch group map to performblock 202. For example, during a topology discovery process, switches inthe fabric may exchange messages to allow the switches toself-configure. For example, in a SAS fabric, expanders may exchangesSMP REPORT GENERAL messages. These configuration messages may includeswitch group identification information. Accordingly, the switch maydetermine to which switch group each other switch belongs. The switchmay also discover each device on the network. For example, in a SASfabric, the switch may discover the initiators and targets connected tothe fabric. The switch may generate the switch group map by mapping eachdevice to the switch group of the switch to which it is directlyconnected. Accordingly, the map may associate the device transmittingthe discovery request received in block 201 with a switch groupidentification number. The switch may compare this switch groupidentification number with its own switch group identification number todetermine if the discovery request originated in the local switch group.

If the discovery request does not originate from the local switch group,the example method may proceed to block 204. Block 204 may includegenerating a discovery response that indicates that there is no deviceat the connection. For example, in a SAS fabric, an expander may returna NO DEVICE ATTACHED message for the PHY listed in the SMP DISCOVERmessage. Accordingly, devices outside the local switch group may beprevented from discovering devices assigned to a reusable zone, whichmay maintain the localized nature of the reusable zone.

If the discovery request does originate from the local switch group, theexample method may proceed to block 203. For example, if the discoveryrequest originates from a second device connected to the local switchgroup, the example method may proceed to block 203. In block 203, theswitch may determine if the requesting device is assigned to a zonepermitted to access the reusable zone. For example, the switch may use azone permission table to determine if the requesting device is assignedto a zone permitted to access the reusable zone.

If the requesting device is in a permitted zone, the method may proceedto block 205. Block 205 may include generating a discovery response thatindicates that the device is connected at the connection. For example,in a SAS fabric, an expander may respond with an SMP DISCOVER RESPONSEframe with information regarding the PHY and the device attached to thePHY.

If the requesting device is not in a permitted zone, the method mayproceed to block 204. As described above, block 204 may includegenerating a discovery response that indicates that there is no deviceat the connection.

FIG. 2B illustrates an example method of providing a discovery responsefor a device assigned to a non-reusable zone. For example, a switch in anetwork fabric may perform the example method illustrated in FIG. 2Aafter receiving a discovery response for a device in a reusable zone andmay perform the example method illustrated in FIG. 2B after receiving adiscovery response for a device in a non-reusable zone.

Block 206 of the example method may include obtaining a second discoveryrequest originating from a second device for a second connection to athird device assigned to a non-reusable zone. For example, in a SASfabric, an expander may perform block 206 by receiving a SerialManagement Protocol (SMP) DISCOVER request for a second PHY connected toa third device assigned to a non-reusable zone. As another example, aswitch may perform block 201 by receiving a second discovery request fora second port connected to a third device assigned to a non-reusablezone.

Block 207 of the example method may include determining if the seconddiscovery request originates in the local switch group. For example, ina SAS fabric, an expander may determine if the second discovery requestwas transmitted by a second initiator device connected to anotherexpander in the local switch group. In some implementations, block 207may be performed in a manner similar to block 202. For example, theswitch may use the switch group map to perform block 207.

If the second discovery request originates from a second deviceconnected to the local switch group, the method may proceed to block210. In block 210 the switch may determine if the second device is in apermitted zone permitted to access the non-reusable zone. In someimplementations, block 210 may be performed in a manner similar to block203. For example, an expander may use a permission table to determine ifthe second device is in a zone permitted to access the non-reusablezone.

If the second device is in a permitted zone, then the method may proceedto block 211. In block 211, the switch may generate a discovery responseindicating that the third device is connected at the second connection.In some implementations, block 211 may be performed in a manner similarto block 205. For example, an expander may response with an SMP DISCOVERRESPONSE frame with information regarding the PHY and the device in thenon-reusable zone that is attached to the PHY.

If the second device is not in a permitted zone, then the method mayproceed to block 208. In block 208, the switch may generate a discoveryresponse that indicates that there is no device at the secondconnection. In some implementations, block 208 may be performed in amanner similar to block 204. For example, an expander may return a NODEVICE ATTACHED message for the second PHY.

If the discovery request does not originate in the local switch group,the method may proceed to block 209. Block 209 may include determiningif the second device is assigned to a non-reusable zone. For example, aswitch may use a listing of the reusable zones and the non-reusablezones to determine if the second device is assigned to a non-reusablezone.

If the second device is assigned to a non-reusable zone, then the methodmay proceed to block 210. In block 210, the switch may determine if thesecond device is in a permitted non-reusable zone that is permitted toaccess the non-reusable zone of the third device. If so, the method mayproceed to block 211, to generate the second discovery requestindicating that the third device is connected at the second connection.

If the second device is not in a permitted non-reusable zone, then themethod may proceed to block 208. As described above, in block 208, theswitch may generate a discovery response indicating that there is nodevice at the second connection. Similarly, if the second device is notin a non-reusable zone 209 (for example, if the second device is in areusable zone), then the method may proceed to block 208.

FIG. 3 illustrates an example switch 300 including a controller 303 togenerate a discovery response to a discovery request for a deviceassigned to a reusable zone. For example, the example switch 300 may bea SAS expander.

The example switch 300 may include a first transceiver 301 to connect toa device assigned to a reusable zone. For example, the first transceiver301 may comprise a physical or logical SAS expander PHY. The exampleswitch 300 may include a second transceiver 302 to connect to a deviceassigned to a non-reusable zone. For example, the second transceiver 301may comprise a second PHY.

The example switch 300 may also include a management port to receive adiscovery request for the transceiver 301 and to transmit a discoveryresponse. In some implementations, the management port 305 may include athird transceiver 306 to connect to a second switch. For example, themanagement port may be an SMP port formed using a third PHY. In thisexample, the discovery request and response may be SMP frames.

The example switch may include a controller 303 to generate thediscovery response. In some implementations, if the discovery requestdoes not originate from a local switch group, the discovery response mayindicate that there is no attached device connected to the transceiver301. For example, the discovery response may be a NO DEVICE ATTACHEDframe corresponding to the requested PHY. In these implementations, ifthe discovery request originates from a second device connected to thelocal switch group and assigned to a zone permitted to access thereusable zone, then the discovery response may indicate that the deviceis connected to the transceiver 301. For example, the discovery responsemay be an SMP DISCOVER RESPONSE frame including information regardingthe PHY and the attached device.

In some implementations, the management port 305 may receive a firstswitch group identification number. For example, the first switch groupidentification number may be assigned to the switch 300 during a networkconfiguration. In these implementations, the controller 303 maydetermining whether the discovery request originates from the localswitch group by determining if the discovery request originated from asecond device connected to a peer switch that is assigned to a secondswitch group identification number. If the second switch groupidentification number is different from the first switch groupidentification number, the controller 303 may determine that discoveryrequest does not originate from the local switch group.

In some implementations, the controller 303 may generate a mapassociating the second device with the second switch groupidentification number during a topology discovery process. Additionally,the controller 303 may use the map to determine if the discovery requestoriginates form the local switch group.

In some implementations, the switch 300 may include a zone managementport 304 to receive a list of reusable zones in a reusable zone group.In further implementations, the zone management port 304 may receive alist of non-reusable zones in a non-reusable zone groups. In some cases,the zone management port 304 may be an out-of-band network port. Forexample, in a SAS expander, the zone management port 304 may be anEthernet port. In other cases, the zone management port 304 may be anin-band network port. For example, the zone management port 304 may bethe management port 305. In these implementations, the controller 303may use the list of reusable zones to determine that the device isassigned to the reusable zone.

In some implementations, the management port 305 may be to receive asecond discovery request for the second transceiver 302. The seconddiscovery request may originate from a third device connected to anon-local switch group. In these implementations, the management port305 may be to transmit a second discovery response. Additionally, inthese implementations, the controller 303 may generate the seconddiscovery response.

If the third device is assigned to a reusable zone, such as the reusablezone assigned to the device connected to the first transceiver 301 oranother reusable zone, then the second discovery response may indicatethat there is no attached device connected to the second transceiver302. If the third device is assigned to a non-reusable zone that ispermitted to access the non-reusable zone of the device connected to thesecond transceiver 302, then the second discovery response may indicatethat the second device is connected to the second transceiver 302. Insome cases, the controller 303 may use the list of non-reusable zone todetermine if the third device is assigned to the non-reusable zone.

FIG. 4 illustrates an example zone manager 400 including anon-transitory computer readable medium 403 storing instructions forpartitioning a network into switch groups, reusable zones, andnon-reusable zones. For example, the zone manager 400 may be a computerusable be a network administrator to configure a network having reusableand non-reusable zones.

The zone manager 400 may include a process 402 and a non-transitorycomputer readable medium 403 storing instructions. For example, themedium 403 may include a non-volatile memory, such as storage or flashmemory, volatile memory, such as random access memory (RAM), or acombination thereof.

The medium 403 may store instructions 404 that are executable by theprocessor 402 to obtain an accessibility assignment for a plurality ofdevices. For example, in a SAS network, the accessibility assignment maygroup targets and initiators into sets of devices permitted tocommunicate with each other. In some implementations, the accessibilityassignment may be generated by a network administrator by assigningdevices to a proxy zone set that includes more zones than are availablein the network. In further implementations, the zone manager 400 maypresent an interface to the network administrator to allow the networkadministrator to generate the accessibility assignment.

The medium 403 may store instructions 405 that are executable by theprocessor 402 to use the accessibility assignment to partition aplurality of switches into a plurality of switch groups. For example,the processor 402 may use a management port 401 connected to a networkto discover a network topology of a plurality of switches connecting thedevices. For example, the processor 402 may use the management port 401to obtain a topology of expanders in a SAS network. In otherimplementations, the network topology may be provided by the networkadministrator.

In some implementations, the instructions 405 are executable by theprocessor 402 to inspect the accessibility assignment to determinecontinuous switch groups that connect devices that communicate with eachother and only with each other. These devices may be assigned toreusable zones that are local to their respective switch groups.

In some implementations, the instructions 405 are executable by theprocessor 402 to transmit switch group assignments to network switches.For example, the processor 402 may transmit assignments through themanagement port 401.

The medium 403 may also store instructions 406 that are executable bythe processor 402 to partition a set of available zone numbers into areusable zone number group and a non-reusable zone number group. In someimplementations, the processor 402 may use the accessibility assignmentand switch partition to determine the partition into the reusable zonenumber group and non-reusable zone number group. In someimplementations, the partitions are not a complete partition of the setof available zone numbers. For example, a subset of the set of availablezone numbers may be reserved. For example, the reserved zone numbers maybe assigned to the reusable zone number group or non-reusable zonenumber group to accommodate network changes, such as adding devices tothe network.

In some implementations, the instructions 406 are executable by theprocessor 402 to send a list of reusable zone numbers in the reusablezone number group to network switches. The instructions 406 may also beexecutable by the processor 402 to send a list of non-reusable zonenumbers in the non-reusable zone number group to network switches. Forexample, the processor 402 may use the management port 401 to send thelists.

The medium 403 may also store instructions 407 executable by theprocessor 402 to assign a device to the reusable zone number group orthe non-reusable zone number group. In some implementations, if a deviceconnected to a switch group is assigned to the reusable zone numbergroup, then the accessibility assignment indicates that the device is noaccessibly by any device not connected to the switch group. In furtherimplementations, if the device is assigned to the non-reusable zonegroup, then the accessibility assignment indicates that the device isnot accessible by any device assigned to the reusable zone group that isnot connected to the switch group. For example, in theseimplementations, devices in the reusable zone group can only contactdevices in the same switch group.

In some implementations, the instructions 407 may be executable by theprocessor 402 to assign devices to the zone number groups by assigningzone numbers to the devices. For example, the instructions 403 may beexecutable to assign the first device to the reusable zone number groupby assigning a reusable zone number to the first device. Additionally,the instructions 403 may be executable to assign the reusable zonenumber to a second device not connected to the switch group. In thiscase, the first and second device may be mutually inaccessible in theaccessibility assignment. Accordingly, the reusable zone number may beused to designate different zones in different switch groups.

As another example, the instructions 407 may be executable by theprocessor 402 to assign a non-reusable zone number to the first device.In this example, the instructions 407 may be executable to assign thenon-reusable zone number to a second device not connected to the switchgroup. In this example, the first and second device may be mutuallyaccessible in the accessibility assignment. Accordingly, non-reusablezone groups may be used to designate zones that extend across the entirenetwork.

In some implementations, the instructions 407 may be executable by theprocessor 402 to transmit the zone number assignments to the networkdevices and switches. For example, the processor 402 may use themanagement port 401 to transmit the zone number assignments.

In the foregoing description, numerous details are set forth to providean understanding of the subject disclosed herein. However,implementations may be practiced without some or all of these details.Other implementations may include modifications and variations from thedetails discussed above. It is intended that the appended claims coversuch modifications and variations.

1. A method, comprising: obtaining a discovery request for a connectionto a device assigned to a reusable zone; and generating a discoveryresponse, wherein if the discovery request does not originate from alocal switch group, the discovery response indicates that there is nodevice at the connection.
 2. The method of claim 1, wherein: if thediscovery request originates from a second device connected to the localswitch group and assigned to a zone permitted to access the reusablezone, the discovery response indicates that the device is connected atthe connection.
 3. The method of claim 1, further comprising: obtaininga second discovery request originating from a second device for a secondconnection to a third device assigned to a non-reusable zone; andgenerating a second discovery response to the second discovery request,wherein if the second device is connected to the local switch group andis assigned to a permitted zone permitted to access the non-reusablezone, the second discovery request indicates that the third device is atthe second connection.
 4. The method of claim 3, wherein: if the seconddevice is not connected to the local switch group and is assigned to apermitted non-reusable zone permitted to access the non-reusable zone,the second discovery request indicates that the second device is at thesecond connection.
 5. The method of claim 1, further comprising: using amap associating a device transmitting the discovery request with aswitch group identification number to determine if the discovery requestdoes not originate from a local switch group.
 6. A switch, comprising: atransceiver to connect to a device assigned to a reusable zone; amanagement port to receive a discovery request for the transceiver, andto transmit a discovery response; and a controller to generate thediscovery response; wherein: if the discovery request does not originatefrom a local switch group, the discovery response indicates that thereis no attached device connected to the transceiver.
 7. The switch ofclaim 6, wherein if the discovery request originates from a seconddevice connected to the local switch group and assigned to a permittedzone permitted to access the reusable zone, the discovery responseindicates that the first device is connected to the transceiver.
 8. Theswitch of claim 6, further comprising: a second transceiver to connectto a second device assigned to a non-reusable zone; and wherein: themanagement port is to receive a second discovery request for the secondtransceiver originating from a third device connected to a non-localswitch group, and is to transmit a second discovery response; and thecontroller is to generate the second discovery response, wherein: if thethird device is assigned to the reusable zone or another reusable zone,the second discovery response indicates that there is no attached deviceconnected to the second transceiver, and if the third device is assignedto a permitted non-reusable zone permitted to access the non-reusablezone, the second discovery response indicates that the second device isconnected to the second transceiver.
 9. The switch of claim 6, furthercomprising: a zone management port to receive a list of reusable zonesin a reusable zone group; and the controller is to use the list todetermine that the device is assigned to the reusable zone.
 10. Theswitch of claim 6, wherein: the management port is to receive a firstswitch group identification number; the controller is to determinewhether the discovery request originates from the local switch group bydetermining if the discovery request originated from a second deviceconnected to a peer switch having a second switch group identificationnumber different from the first switch group identification number. 11.The switch of claim 10, wherein: the controller is to generate a mapassociating the second device with the second switch groupidentification number during a topology discovery process and to use themap to determine if the discovery request originates from the localswitch group.
 12. A non-transitory computer readable medium storinginstructions executable by a processor to: use an accessibilityassignment for a plurality of devices to partition a plurality ofswitches connecting the plurality of devices into a plurality of switchgroups; and partition a set of available zone numbers into a reusablezone number group and a non-reusable zone number group; and assign adevice to the reusable zone number group or the non-reusable zone numbergroup; wherein, if a device connected to a switch group is assigned tothe reusable zone number group, then the accessibility assignmentindicates that the device is not accessible by any device not connectedto the switch group.
 13. The non-transitory computer readable medium ofclaim 12, wherein: if the device is assigned to the non-reusable zonegroup, then the accessibility assignment indicates that the device isnot accessible by any device assigned to the reusable zone group and notconnected to the switch group.
 14. The non-transitory computer readablemedium of claim 12, storing further instructions executable by theprocessor to: assign the first device to the reusable zone number groupby assigning a reusable zone number to the first device; and assign thereusable zone number to a second device not connected to the switchgroup, the first and second device being mutually inaccessible in theaccessibility assignment.
 15. The non-transitory computer readablemedium of claim 12, storing further instructions executable by theprocessor to: assign the first device to the non-reusable zone group byassigning a non-reusable zone number to the first device; and assign thenon-reusable zone group number to a second device not connected to theswitch group, the first and second device being mutually accessible inthe accessibility assignment.
 16. The method of claim 2, wherein a zonepermission table is used to determine if the requesting device isassigned to the zone permitted to access the reusable zone.
 17. Themethod of claim 3, wherein obtaining a second discovery request isperformed by an expander or a switch.
 18. The method of claim 3, whereinif the second device is not assigned to the permitted zone, the seconddiscovery request indicates that there is no device at the secondconnection.
 19. The switch of claim 8, further comprising a thirdtransceiver to connect to a second switch.
 20. The switch of claim 9,further comprising the zone management port to receive a list ofnon-reusable zones in a non-reusable group.